Defrost cycle controller

Abstract

A defrost controller for a refrigerator/freezer including one or more of the following features: (1) a timer module that can serve as a real time, cumulative time or variable time defrost timer; (2) an algorithm to control defrosting in view of frequent power outages; (3) a power up defrost cycle; (4) a default reaction to loss of compressor run information; (5) a simple manufacturing test initiator; (6) a test initialization via thermostat actuation; (7) a relay power supply which supplies two different energization voltages; (8) a relay energization signal which decays rapidly from a voltage in excess of the relay rated voltage to a voltage within the relay rated voltage; and (9) respective relay energization sequence to overcome light contact welding.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A defrost cycle controller for a freezer system including a compressor whose operation is actuated by a thermostatic switch and a defrost heater whose operation is actuated by a bimetal switch, comprising: a relay operatively connected to mutually exclusively couple the compressor and the defrost heater to a power supply;   a first signal line providing a first signal indicative of the operating status of the compressor;   a second signal line providing a second signal indicative of the operating status of the defrost heater;   a microprocessor operatively coupled to the first and second signal lines and to the relay to control energization of the relay and to select coupling of the compressor and the defrost heater to the power supply, the microprocessor being programmed to sense the first and second signals and vary the length of intervals during which the compressor and defrost heater are coupled to the power supply, the microprocessor being programmed to couple the defrost heater to the power supply after times determined by preselected continuous compressor run periods and preselected cumulative compressor run periods.   
     
     
       2. The defrost cycle controller of claim 1, wherein the microprocessor is programmed to couple the defrost heater to the power supply only after the compressor has accumulated ten hours of run time. 
     
     
       3. A defrost cycle controller for a freezer system including a compressor whose operation is activated by a thermostatic switch and a defrost heater whose operation is activated by a bimetal switch, comprising: a relay operatively connected to mutually exclusively couple the compressor and the defrost heater to a power supply;   a first signal line providing a first signal indicative of the operating status of the compressor;   a second signal line providing a second signal indicative of the operating status of the defrost heater; and   a microprocessor operatively coupled to the first and second signal lines and to the relay to control energization of the relay and to select coupling of the compressor and the defrost heater to the power supply, the microprocessor being programmed to sense the first and second signals and to vary the length of intervals during which the compressor and defrost heater are coupled to the power supply, the microprocessor being programmed to couple the defrost cycle heater to the power supply after preselected decreasing continuous compressor run periods as preselected increasing cumulative compressor run times are reached.   
     
     
       4. The defrost cycle controller of claim 3, wherein the preselected continuous compressor run times and preselected cumulative compressor run periods are correlated as follows:   ______________________________________                                    
                  Continuous Compressor                                   
                  Run Time Which Will                                     
Cumulative Compressor                                                     
                  Trigger Coupling of Defrost                             
Run Time          Heater to Power Supply                                  
______________________________________                                    
From 10 to less than 15                                                   
              hours   2          hours                                    
From 15 to less than 20                                                   
              hours   1.5        hours                                    
20 or more    hours   1          hour                                     
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       5. A method of reducing sensitivity of a freezer controller to power outages, comprising the steps of: providing a freezer controller which is configured to control operation of a compressor and a defrost heater to monitor demand for the operation of the compressor and the defrost heater via status of a thermostat and status of bi-metal switch powering up the freezer controller;   after a predetermined interval, determining the status of the thermostat;   if the thermostat indicates need for cooling, setting compressor run time to a first reduced predetermined value;   if the thermostat indicates no need for cooling, actuating the defrost heater and after a predetermined time period, setting the compressor run period to a second predetermined time period.   
     
     
       6. The method of claim 5, wherein the first predetermined value is six hours. 
     
     
       7. The method of claim 6, wherein the second predetermined value is eight hours.